High temperature dry desulfurization technology is technology removing sulfur ingredients such as H2S, COS in fuel gas generated from coal gasification or synthetic gas at a high temperature with a dry state. The high temperature dry desulfurization technology has an advantage of having no waste water treatment in an environmental aspect compared to low temperature wet desulfurization technology using absorbent of amine type which is widely used in a general chemical plant, where a sulfur ingredient may be removed in high temperatures of 400-600° C., cooling of the synthetic gas may not be needed compared to the wet desulfurization technology operated at low temperature (below 100° C.), reducing sensible heat, thereby increasing power generation efficiency.
In particular, in the case of an Integrated Gasification Combined Cycle (IGCC), sulfur ingredients included in fuel gas must be reduced less than dozens of ppmv in order to prevent corrosion of a gas turbine, and in the case of an Integrated Gasification Fuel Cell (IGFC) sulfur must be reduced to ppbv level in order to prevent poisoning of catalyst and degradation of the electrode.
The high temperature dry desulfurization technology is technology which selectively absorbs H2S and COS when high temperature and high pressure fuel gas (or synthetic gas) contacts with a desulfurizing agent in a solid state. Composition of synthetic gas emitted by coal gasification may be changed according to the type of the coal gasification and composition of coal; however, representatively, composition of synthetic gas emitted by a coal gasifier of Shell is 65% of CO, 1.5% of CO2, 29.5% of H2, 4% of N2 and also includes H2S and COS.
FIG. 1 illustrates a diagram of a conventional apparatus for desulfurization and FIG. 2 illustrates a flowchart of an operating method of the conventional apparatus for desulfurization. Like this, in order to remove sulfur ingredients in the synthetic gas, the high temperature dry desulfurization technology, as illustrated in FIG. 1, includes two reactors, that is, a desulfurization reactor and a regeneration reactor.
As illustrated in FIG. 1, the synthetic gas including the sulfur ingredients is injected through a synthetic gas inlet of a lower portion of the desulfurization reactor, and is to be contacted with solid desulfurizing agent particles which enable removing the sulfur ingredients in the reactor. For the desulfurizing agent, Zn, Fe, Ni, Co, Mn, Ce, or oxide thereof, or mixtures thereof are used, or bentonite, alumina, zeolite, silica, hexaaluminate, zirconia, or depressor fabricated by using mixtures thereof as a support may be used.
Representatively, in the case that Zinc oxide is used as the desulfurizing agent, within the desulfurization reactor, the sulfur ingredients H2S and COS are absorbed into the desulfurizing agent by the reaction such as the following Formula 1 and Formula 2 and are to be emitted as H2O or CO2.H2S+ZnO=ZnS+H2O  [Formula 1]COS+ZnO=ZnS+CO2  [Formula 2]
Further, the desulfurizing agent that absorbed the sulfur ingredients and the synthetic gas with the removed the sulfur ingredients are emitted through outlet 12 of an upper portion of desulfurization reactor 10 and flowed into a desulfurization cyclone 20 (S2), and the synthetic gas with the removed the sulfur ingredients are divided into gas and solid in the desulfurization cyclone 20 and the gas is emitted through gas outlet 21 of an upper portion of the desulfurization cyclone, and desulfurizing agent particles (solid) that absorbed the sulfur are emitted through solid outlet 22 of a lower portion of the desulfurization cyclone and are introduced to the regeneration reactor 30 (S3).
In the regeneration reactor 30, ZnO and SO2 are obtained by oxidizing ZnS by injecting oxidizing agent (oxygen or air) to oxidizing agent inlet 32 of a lower portion of the regeneration reactor as like below Formula 3, and oxidized desulfurizing agent particles are recirculated to the desulfurization reactor by discharging them from the desulfurizing agent outlet 33.ZnS+1.5 O2=ZnO+SO2  [Formula 3]
The desulfurizing agent emitted from the regeneration reactor 30, SO2, and other gases are introduced in regeneration cyclone 40 by emitting them through regeneration reactor outlet 34 (S4), SO2, and other gases are emitted through gas outlet 41 of an upper portion of the regeneration cyclone by dividing air and solid in the regeneration cyclone 40, and the desulfurizing agent recirculates from the solid outlet 42 of a lower portion of the regeneration cyclone 40 and is flowed into recirculation inlet 35 of the regeneration reactor (S5).
In addition, SO2 and other gases emitted in the regeneration reactor 30 and emitted through the gas outlet of the regeneration cyclone as illustrated in FIG. 1, are introduced in the Direct Sulfur Recovery Process (DSRP) reactor 50, and within sulfur recovery reactor 50 charged with catalyst, they are recovered through sulfur outlet 52 in a form of elemental S by a reaction of the following Formulas 4 and 5, and air CO2 and H2O are emitted through gas outlet 53 (S6).SO2+2CO=2CO2+S  [Formula 4]SO2+2H2=2H2O+S  [Formula 5]
In the sulfur recovery reactor 50, reductive gases CO, H2, etc., which are needed to direct the sulfur recovery reaction may be injected separately; however, CO and H2 included with the synthetic gas may be used, therefore, as illustrated in FIG. 1, part of the synthetic gas with removed sulfur ingredients emitted through the gas outlet 21 of the desulfurization cyclone 20 may be used.
For this high temperature dry desulfurization technology, because desulfurizing agent having solid particles must continuously circulate between the desulfurization reactor 10 and the regeneration reactor 30, a fluidized bed type reactor is generally used, and in the case of the direct sulfur recovery process, a fixed bed type reactor charged with the catalyst is mostly used.
In a high temperature dry desulfurization apparatus like FIG. 1, oxygen is needed to regenerate the desulfurizing agent that absorbed the sulfur ingredients, because air injection is advantageous with respect to cost rather than pure oxygen injection, the air injection is common in general.
In the case of the air injection, air may must be injected with as much oxygen as needed for the regeneration reaction of the desulfurizing agent; however, it may be changed only within the scope of the change of gas velocity of the regeneration reactor 30 to be operated in a fluidized bed state, and excess oxygen injection is advantageous in order to complete regeneration of the desulfurizing agent, therefore, in gas emitted in the regeneration reactor 30 and flowed into the direct sulfur recovery process the oxygen is to be included with SO2.
In the case that the oxygen is injected in the direct sulfur recovery process, reductive gas which is to reduce SO2 to elemental S is consumed because a combustion reaction of CO and H2 as like following Formulas 6 and 7 is to occur rather than the reaction in aforementioned Formulas 4 and 5, therefore, sulfur recovery efficiency may be decreased, and the combustion reaction of CO and H2 is the exothermic reaction, and a temperature of the catalyst layer is increased drastically, therefore, decreased activity by thermal shock and deterioration of catalyst may occur.CO+0.5 O2=CO2  [Formula 6]H2+0.5 O2=H2O  [Formula 7]
Therefore, in the case that the oxygen is flowed into the direct sulfur recovery process, efficiency of a catalyst reaction may be decreased and it may influence stability of the process, therefore, it is important to minimize the flowed oxygen concentration. However, in order to increase efficiency of the regeneration of the high temperature dry desulfurization process regeneration reactor 30, a high oxygen concentration is advantageous; therefore, a method for increasing efficiency of both processes was required.